1. Field of the Invention
The present invention relates to the preparation of chloroalkoxybenzenes, and, more especially, to the preparation of chloroalkoxybenzenes from chlorobenzene starting materials.
2. Description of the Prior Art
It is known to this art to prepare chloroalkoxybenzenes from chlorobenzene precursors. Thus, the preparation of 2,3-dichloroanisole by reaction of sodium methylate with 1,2,3-trichlorobenzene in methanol, at a temperature of 180.degree. C. and under pressure, has been described [Recueil des Travaux Chimiques des Pays-Bas (Reports of Chemical Work in the Netherlands), 37, 200]. Such process, however, is not applicable on an industrial scale, because numerous by-products result therefrom and the yields obtained are very low.
And in U.S. Pat. No. 4,057,585 there is described the preparation of 2,3-dichloro-1-alkoxybenzene by reacting an alkali metal lower alkoxide with 1,2,3-trichlorobenzene, at 100.degree.-200.degree. C., in an inert solvent selected from the group consisting of dimethylformamide, dimethylacetamide and dimethylsulfoxide, the reaction taking place in the presence of methanol or ethanol in amounts sufficient to solvate the alkali metal alkoxide. In this particular type of process, two major disadvantages militate against the industrial application thereof. The first is predicated upon the fact that it is necessary to employ a completely anhydrous alkali metal alkoxide, thus prepared from the corresponding alkali metal in metallic form. Indeed, an alkoxide devoid of sodium hydroxide must be utilized, lest the NaOH degrade the solvent medium. The second disadvantage resides in the fact that the required solvents are on the one hand, burdensome, and on the other are but poorly adapted for use on an industrial scale, by reason of the necessity for the distillation and recycling thereof.
Further, in Sam and Simmons, Journal of the American Chemical Society, 96, No. 17, p. 2252 (1974), there is disclosed the reaction of o- or m-dichlorobenzene with potassium methylate complexed with an equimolecular amount of a crown ether (18-dicyclohexyl-6-crown). This technique is not especially worthwhile, though, both by reason of the economy of the process, and, secondly, because of the complexity thereof. Indeed, "crown ethers" are quite costly compounds. Furthermore, it too is necessary to prepare the crown ether-alcoholate complex in a separate step.